Pressure sensing catheters are used in a variety of medical procedures. Such catheters can be employed to sense pressure in rectal or urodynamic applications, being positioned within the urethra or bladder or another internal location within the body. Pressure-sensing catheters may also be applied to the rectum, vagina, or another internal location within the body in which pressure readings are desired. With reference to FIG. 1, a pressure sensing catheter 100 according to a typical prior art implementation is shown. In this example, the catheter 100 has been inserted transurethrally into the subject patient's bladder 110. While not shown, it can be assumed that the bladder is filled with urinary fluid under predetermined pressure that may be in excess or ambient atmospheric pressure. The catheter shaft 101 may be 7 French in diameter (approximately 0.096 inch), allowing it to pass relatively easily through the urethra. The distal end 112 of the exemplary catheter 100 includes a single pressure-sensing balloon 114 according to the prior art. The balloon is pliable, polymeric membrane that defines a predetermined interior space with respect to the underlying, semi-rigid catheter shaft 101. The balloon 114 is attached in a fluid-tight manner to the catheter shaft's outer surface using adhesives or another attachment technique. The interior space of the balloon 114 (defined between the catheter's outer surface and the balloon's inner wall) communicates with an inner lumen (not shown) that allows fluid/pressure to pass between the balloon enclosure and the proximal end 116 of the catheter 100.
The catheter's proximal end 116 includes a standard fitting 120 that is sized and arranged to receive the fluid-dispensing distal end 130 of a conventional fluid syringe 132 having a plunger assembly 134 and a fluid-containing/dispensing barrel 136. The syringe 132 can be filled with any inert, biocompatible fluid, such as normal saline. The volume of the syringe 132 is typically sufficient to fill the lumen of the catheter and the balloon 114. In use, the catheter 100 is guided into the urethra, bladder or another body cavity in which localized pressure measurement is desired. Typically, following insertion, the syringe 132 containing fluid, is applied to the proximal fitting 120. The fluid is then directed into the lumen so as to at least partially fill the balloon 114 and interconnected lumen. A proximal side port (not shown) communicating with the lumen may allow for the expulsion of air as fluid fills the catheter balloon and lumen. After a predetermined quantity of fluid is introduced to fill the space, the syringe may be removed from the fitting 120 and another syringe not shown) is applied to the fitting. The plunger of the second syringe is drawn proximally, out of the barrel to create a low-pressure vacuum at the inlet of the catheter. The vacuum allows air bubbles within the lumen and the balloon 114 to be evacuated. It is desired that all air bubbles be removed from the lumen and balloon before a pressure reading is taken. This may entail multiple cycles of filling and vacuum-application until the practitioner is fairly certain that no air bubbles remain. Due to the small diameter of the lumen, air bubbles may have a tendency to adhere to the luminal walls due to surface tension. Thus, removal of all bubbles may require several fill and vacuum-application cycles. Tapping the catheter shaft 101 to jar adhering bubbles may also be desirable. Once bubbles have been removed from the catheter 100, the proximal end fitting 120 (or another connection) is connected to a pressure transducer assembly 140. The transducer assembly includes a mating fluid fitting 142 on the end of the transducer housing 142 that is sized to mate with the catheter proximal fitting 120. Within the transducer assembly's housing, in communication with the inlet of the fitting 142, is a fluid-impermeable membrane (not shown) that communicates with an electronic transducer element. The transducer element and its associated internal electronics are electrically connected by a multi-pin connector 146 to a cable 148. The cable 148 extends a predetermined distance to an opposing connector 150 that interfaces with an appropriate electronic device 160. The electronic device 160 can include a pressure value readout 162 of appropriate scale and type, as well as other control electronics and power supply systems.
The above-described system and method for employing a pressure sensing catheter and sensing internal body pressure has several disadvantages. In particular, the practitioner must fill the catheter lumen and balloon with an appropriate level of fluid, and then ensure removal of any air bubbles. This is a time-consuming process, and may lead to inaccuracies if air bubbles remain. It may be difficult to determine whether residual air bubbles are present in the filled catheter, particularly when the catheter is already inserted into the patient. In addition, the extra time required to fill the catheter with fluid means that the patient must endure a longer procedure-particularly where the catheter is first introduced to the patient's body, and then filled with fluid. Moreover, the subsequent connection of the catheter's pressure transducer assembly makes it more likely that the system will experience air bubbles or leaks, after it is filled. All of these disadvantages lead to a more time-consuming and potentially less-accurate procedure.
Accordingly, it is desirable to provide a pressure sensing catheter, and method for using such a catheter, that avoids time-consuming and inaccuracy-producing steps. Moreover, it would be desirable to provide a catheter that reliably allows for multiple pressure readings at different locations along its length without the need of multiple balloon-filling steps to be undertaken by the practitioner. Furthermore, such a catheter should provide for easy and quick connection to conventional pressure-sensing display electronics and should allow for an infusion/flushing connection to deliver fluid to the patient from a distal location along the catheter.